Mirror replacement in Durst 138 enlarger - special or not?

Hi - the mirror in my Durst 138 enlarger is deteriorating to the point where I would like to replace it. Is it a special kind of mirror/glass or will any reasonable kind of mirror be good enough? The heat absorbing glass is in tact in the housing FYI.
If it is a special kind of mirror is there a generic name for it that I could give to my local glass/mirror guy? Appreciate any advice, tips or your experience in a similar situation. Thanks.

I believe Durst employs a rear silvered mirror not a front surface mirror. My Durst F60 had a similar degradation to its mirror and I went to a hobby shop and bought a thin mirror and a glass cutter and it worked out great.

Something like this. I only needed 4x4 inches. The one you have is larger I am bet

Thanks for the link Andy. I now know probably more than I really need to know about first surface and second surface mirrors after some further googling! I had a good look at the mirror and it is a second surface standard mirror as far as I can tell so should be able to replace for not much money. It is 21cm square (8 1/4 inch) as you might expect to cover 5x7 negative. Cheers
Tony

Woohooooo! Being new round here it sure is nice to have finally helped someone!
First surface, second surface.....good gosh, who knew it mattered till your mirror goes bad, glad Apug has the answers! Best of luck!

Pretty ambiguous question unless you specify what kind of head is on this enlarger. 138 is the Durst
chassis series, and many different heads were made for this. I have seen mirrors that were not even
glass but multicoated front-surface machined optical quartz to take high temps (probably not what
you've got) - but some ordinary mirror silverings would probably catch fire.

It's the basic 5x7 condenser head. I found a local mirror cutter and I'll take the old one along to the shop as well to get an opinion. I can't be sure the current mirror is the original but it is certainly old and getting a bit crusty in places.

I have used a cheap craft store mirror cut to size in the 138/S45. I was getting some dark banding from the standard Durst mirror when using a halogen point source bulb. The craft store mirror actually worked better in this case. I doubt that you would see any difference with an opal bulb. BTW, I glued strips of 3/16" masonite to the back of the mirror to hold it in place after closing the door -- otherwise it wants to slide down slightly and won't remain at a 45 degree angle.